Embryologically, the human lens forms with a fetal nucleus which, after development, becomes the center of the crystalline lens. The inner side of the anterior capsule of the lens contain epithelial cells which migrate peripherally and posteriorly to lay down concentric lamellae of nuclear tissue. An adult nucleus next forms around the fetal nucleus and concentrically disposed lamellae, and the lens takes shape.
Throughout life, the epithelial cells continue to migrate and lay down lamellae of nuclear tissue. However, because the lens is now enclosed by the adult nucleus, the area of lens growth is confined causing the layers to become compressed and tightly packed. This increased compression and packing causes the lens to become stiff and firm, and by the age of 40 the ability of the lens to flex and focus is greatly reduced. As successive layers continue to be deposited, the lens becomes so dense that it begins to change color and the clarity is lost. At this point, the successively deposited layers of lamellae are referred to as a cataract. The inner nucleus of the cataract consists of a firm, dense material while the outer nucleus consists of a less dense material. The material surrounding the nucleus of a cataractous lens is known as the cortex.
Different terms are used to describe the surgical steps of separating the nucleus into its various components. Hydrodissection usually refers to an irrigation of fluid between the anterior capsule and the outer nucleus, essentially separating the outer nucleus from the cortex and even separating some cortex from itself.
The terms hydrodelineation, hydrodelamination, and hydrodemarcation are all synonymous and refer to the injection of fluid within the body of the cataract to separate the inner nucleus from the outer nucleus. In some instances, it is possible to cause multiple separations of the inner nucleus into several nuclei. This multiple separation is referred to as multilamellar delineation.
The instruments typically used to perform this function are blunt tipped cannulas generally between 25 and 30 gauge in diameter. The cannulas are attached to a syringe containing a balanced salt solution. During surgery, the rounded tip of the cannula is thrust into the wall of the capsular bag and into the lens therein to obtain a cleavage plane. A salt solution is injected into the cataract and the nucleus of the lens is hydrodelineated and decompacted.
Multilamellar delineation during the surgical phase of hydrodelineation may be accomplished using hydrosonics based on technology licensed to Alcon Corporation by Azis Aniz, M.D. A small needle is attached to an ultrasonic handpiece and high frequency ultrasound activates the tip, permitting deep penetration of the nucleus. A salt solution is injected into the nucleus and several cleavage planes (multilamellar delineation) are obtained due to the vibrating tip coming in contact with several lamellae. Unfortunately, this device costs just under $20,000.
A needle useful in ophthalmic surgery is disclosed by Thorton et al., U.S. Pat. No. 4,808,170. The needle is designed to administer posterior peribulbar or retro-bulbar anesthesia and contains a beveled tip on the distal end of the needle. The object of the needle is to penetrate by separating tissue instead of cutting tissue, therefore the tip and sides of the tip are rounded to provide a smooth transition between the bevel tip and side surfaces of the needle.
Straus, U.S. Pat. No. 4,759,746, discloses a retro-bulbar needle. The needle is for use in administering retro-bulbar or peribulbar anesthetics. The curved needle extends outwardly away from the longitudinal axis of the hub and then extends inwardly towards the longitudinal axis concluding with a terminal section which is straight and oriented at a predetermined angle to the longitudinal axis. The tip of the needle is rounded and beveled and the bevel is towards the concave aspect of the curved needle. The needle is curved so as to reduce the risk of retro-bulbar hemorrhage by violating less orbital space.
There are several structures of needles disclosed in other arts similar in construction to the apparatus disclosed herein such that they warrant discussion although they do not anticipate or make obvious the present invention. One such needle is disclosed by Yanus, U.S. Pat. No. 2,601,580. A portion of the needle shank is flattened by rollers to reduce the pain incurred by a patient when an otherwise rounded needle of equivalent cross sectional area is used. Also, the needle is beveled at the distal end and the beveled sides are sharpened to function as cutting edges.
Ginsburg, U.S. Pat. No. 2,899,959, discloses a hypodermic needle. The needle comprises a shank wherein the upper and lower shank sections are substantially parallel to each other and the axis of the intermediate part of the shank forms an obtuse angle with the axis of the upper section and an obtuse angle with the lower section. Also, the tip of the lower shank portion is beveled. The structure disclosed by Ginsburg helps to reduce problems normally associated with straight shanks such as the insertion point frequently scratching the vein walls causing pain, excessive limb movement causing the needle to slip out, and potential that a straight shank will not properly position itself for injection or withdrawal of blood.
Froning, U.S. Pat. No. 4,013,080, discloses a cannula connector useful in lumbar disc puncture. When the cannula is in proximity to the disc to be treated, a disc penetrating needle is inserted into the lumen o the cannula. The needle has a male luer-lock fitting for attachment to a syringe at its proximal end and a beveled tip at the distal end. The terminal section of the needle is also curved. The terminal section of the needle is curved to facilitate the maneuverability of the needle around obstacles.
While the prior art needles disclose structures with rounded beveled tip, curved shanks and flattened portions (in certain combinations), these needles are not suitable for obtaining multilamellar delineation during the cataract surgery phase of hydrodelineation/hydrodelamination/hydrodemarcation. One such method of achieving multilamellar delineation is through the hydrosonics device licensed to Alcon Corporation by Azis Aniz, M.D., however, this device is expensive as was noted previously.
Thus, there is a need for an inexpensive cannula for use in cataract surgery during the surgical phases of hydrodissection and hydrodelamination/hydrodelineation/hydrodemarcation.
Therefore, it is a primary object of this invention to provide an economically disposable cannula for use in cataract surgery during the surgical phases of hydrodissection and hydrodelamination/hydrodelineation/hydrodemarcation.
Another object of this invention is to provide an inexpensive cannula for use in cataract surgery that will isolate several cleavage planes (multilamellar delineation) during the surgical phase of hydrodelamination/hydrodelineation/hydrodemarcation.
A further object of this invention is to provide a curved cannula for use in cataract surgery that will permit better control of the instrument during the surgical phase of hydrodissection.
Another object of this invention is to provide a cannula for use in cataract surgery with a flattened shank section to rotate the nucleus during the surgical phases of hydrodelamination/hydrodelineation/hydrodemarcation and obtain improved cleavage of the nucleus when compared to circular cross-sectional cannulas.
Another object of this invention is to provide a cannula with a short length of needle to enable the cannula hub to be close to the eye thereby reducing unwanted leverage.
Still another object of this invention is to provide a cannula with a rounded tip and sharpened sides to engage, penetrate and irrigate additional tissue.